To spy on a human rights activist, hackers allegedly connected to a Middle Eastern government used three previously unknown vulnerabilities in Apple’s iOS.

The claims -- from research at Toronto-based Citizen Lab and mobile security firm Lookout -- focus on spyware that targeted Ahmed Mansoor, an activist in the United Arab Emirates.

Earlier this month, Mansoor received an SMS text message on his iPhone claiming to offer “new secrets” about tortured detainees in his country. However, inside the message was a link that, once clicked, can infect an iPhone with spyware, using three zero-day exploits of iOS, the research found.

The exploits work by remotely jailbreaking the device to secretly download the spyware – which can then access the iPhone’s camera, microphone, and messages.

Lookout called the attack the most sophisticated it’s ever seen on a device. The researchers have already informed Apple about the exploits, and iOS version 9.3.5 -- which was released on Thursday -- fixes the issues.

The attack is rare because it used three previously unknown vulnerabilities, suggesting the hackers were well-funded. Just one of these exploits can be worth US$1 million.

Citizen Lab, however, is pointing fingers at an Israeli security firm called NSO Group, which reportedly specializes in monitoring smartphones of government targets.

NSO Group doesn’t maintain a website, and an email to the company went unanswered. But Citizen Lab said leaked documents appear to show the Israeli company selling a spyware product called Pegasus, which matches with the three zero-day exploits found.

Citizen Lab also analyzed the domain name in the link Mansoor received via SMS text message. Following a long internet trail, it found an NSO Group registered email as part of evidence tying the Israeli company to the attack.

The UAE likely hired NSO Group to spy on Mansoor, Citizen Lab added. Mansoor has previously been the target of commercial spyware back in 2011 and 2012.

“While these spyware tools are developed in democracies, they continue to be sold to countries with notorious records of abusive targeting of human rights defenders,” said Citizen Lab, which is based out of the University of Toronto.